Neurotransmitters are the chemical substances that mediate information transfer between cells in the nervous system. These substances are released at synaptic terminals and interact with specific receptors on postsynaptic cells. The goal of this research is to screen for neurotransmitters in lateral neurons of the mammalian visual system and to develop autoradiographic procedures for identifying cholinergic neurons. The procedure for transmitter screening is based on axonal transport. Radioactive transmitter precursors will be pressure-injected into regions of physiologically-identified cell bodies. Radioactive substances, axonally transported to specific neuron terminals, will be identified biochemically, then tested for fulfillment of various other criteria for neuro-transmitter function such as localization, release, and physiological and pharmacological response. Autoradiographs of spinal cords injected with (3H) choline show selective accumulation of label, probably in the form of choline lipid, over motoneuron pericaryia, axons, and dendrites. The metabolic significance of this accumulation will be examined to determine if it could serve as the basis for an autoradiographic method for tracing cholinergic neurons. In vivo injections and explant cultures will be used to determine if other cholinergic neurons are similarly selectively labelled. Parallel biochemical investigations will identify the observed compounds and determine their relationship to acetycholine metabolism.